Bearing device for driving wheel

ABSTRACT

A driving-wheel bearing device includes: an outer race ( 50 ) having double-row outer raceway surfaces ( 52, 54 ) formed on an inner periphery thereof; a hub wheel ( 10 ) and an inner race ( 20 ) having a wheel attachment flange ( 14 ) at one end thereof and double-row inner raceway surfaces ( 12, 22 ) on an outer periphery thereof; and double-row rolling elements ( 30, 40 ) interposed between the outer raceway surfaces ( 52, 54 ) of the outer race ( 50 ) and the inner raceway surfaces ( 12, 22 ) of the hub wheel ( 10 ) and the inner race ( 20 ), the hub wheel ( 10 ) having a shaft hole into which a stem section ( 66 ) extending from an outer joint member ( 62 ) of a constant velocity universal joint ( 60 ) is spline-fitted by being press-fitted, in which a plate ( 80 ) having a molybdenum coating layer or a fluorine-resin coating layer ( 81 ) formed thereon and having a plate thickness ranging from 0.5 mm to 2 mm is interposed between opposite surfaces of a shoulder portion ( 61 ) of the outer joint member ( 62 ) and an crimped portion ( 13 ) of the hub wheel ( 10 ).

TECHNICAL FIELD

The present invention relates to a driving-wheel bearing device whichrotatably supports a driving wheel (front wheel of a front-enginefront-drive (FF) vehicle, rear wheel of a front-engine rear-drive (FR)vehicle, and all wheels of a four-wheel drive (4WD) vehicle) withrespect to a suspension device for, for example, an automobile.

BACKGROUND ART

Bearing devices for automobiles include ones for driving wheels and onesfor driven wheels, and there have been proposed ones of various types inaccordance with respective applications. For example, FIG. 16illustrates a driving-wheel bearing device. The bearing device includesthe following as main components: a hub wheel 210 and an inner race 220,double-row rolling elements 230 and 240, an outer race 250, and aconstant velocity universal joint 260.

The hub wheel 210 has an outboard-side inner raceway surface 212 formedon an outer peripheral surface thereof, and includes a wheel attachmentflange 214 for allowing a wheel (not shown) to be attached thereto. Hubbolts 216 for fixing a wheel disk are equiangularly embedded in thewheel attachment flange 214. The inner race 220 is fitted to asmall-diameter step portion 218 formed on the outer peripheral surfaceof the hub wheel 210, and an inboard-side inner raceway surface 222 isformed on an outer peripheral surface of the inner race 220. A femalespline 211 for coupling the constant velocity universal joint 260 withthe hub wheel 210 so that torque can be transmitted therebetween isformed on an inner peripheral surface of a shaft hole of the hub wheel210.

The inner race 220 is press-fitted to the small-diameter step portion218 of the hub wheel 210 with adequate tightening margin for the purposeof preventing creep. The outboard-side inner raceway surface 212 formedon the outer peripheral surface of the hub wheel 210 and theinboard-side inner raceway surface 222 formed on the outer peripheralsurface of the inner race 220 constitute double-row inner racewaysurfaces. The inner race 220 is press-fitted to the small-diameter stepportion 218 of the hub wheel 210, and the end portion of thesmall-diameter step portion 218 of the hub wheel 210 is crimped outward.As a result, the inner race 220 is prevented from slipping off by acrimped portion 213 thus formed, and is integrated with the hub wheel210, to thereby apply preload to a bearing section 270.

The outer race 250 has double-row outer raceway surfaces 252 and 254formed on an inner peripheral surface thereof and opposed to the innerraceway surfaces 212 and 222 of the hub wheel 210 and the inner race220, and includes a vehicle body attachment flange 256 for beingattached to a vehicle body (not shown). The vehicle body attachmentflange 256 is fixed, with use of an attachment hole 258, by bolts or thelike to a knuckle extending from a suspension device (not shown) of avehicle body.

The bearing section 270 has a double-row angular ball bearing structure,specifically, has the following structure: the rolling elements 230 and240 are interposed between the inner raceway surfaces 212 and 222 formedon the outer peripheral surfaces of the hub wheel 210 and inner race 220and the outer raceway surfaces 252 and 254 formed on the innerperipheral surface of the outer race 250; the rolling elements 230 and240 in respective rows are rotatably and equiangularly retained byretainers 232 and 242.

At the openings on both ends of the bearing section 270, a pair of seals234 and 244 for sealing annular spaces between the outer race 250 andthe hub wheel 210 and between the outer race 250 and the inner race 220so as to be held in sliding-contact with the outer peripheral surfacesof the hub wheel 210 and inner race 220 are fitted to the innerperiphery at both end portions of the outer race 250. Further, the seals234 and 244 prevent leakage of lubricant filling the inside andintrusion of water and foreign matters from the outside.

An outer joint member 262 of the constant velocity universal joint 260is coupled with the hub wheel 210, and hence a bearing device isconstituted. The outer joint member 262 of the constant velocityuniversal joint 260 is provided at one end of an intermediate shaft (notshown) constituting a drive shaft, and is constituted by the following:a cup-shaped mouth section 264 housing inner components (not shown)including an inner joint member, balls, and a cage; and a stem section266 extending integrally from a proximal portion of the mouth section264 in an axial direction. A male spline 268 for coupling the hub wheel210 with the constant velocity universal joint 260 so that torque can betransmitted therebetween is formed on an outer peripheral surface of thestem section 266.

The stem section 266 of the outer joint member 262 is press-fitted tothe shaft hole of the hub wheel 210, and the male spline 268 formed onthe outer peripheral surface of the stem section 266 and the femalespline 211 formed on the inner peripheral surface of the shaft hole ofthe hub wheel 210 are fitted to each other. In this manner, torque canbe transmitted. Further, in a state in which opposite surfaces of thecrimped portion 213 of the hub wheel 210 and a shoulder portion 261 ofthe outer joint member 262 are hit against each other, a nut 272 istightened to a male-screw portion 265 formed at an end portion of thestem section 266. In this manner, the constant velocity universal joint260 is fixed to the hub wheel 210.

Incidentally, in the driving-wheel bearing device, the crimped portion213 of the hub wheel 210 of the bearing section 270 and the shoulderportion 261 of the outer joint member 262 are in a contact state ofbeing hit against each other. Thus, upon starting of a vehicle, there isa risk that stick-slip noise commonly known as squeaking noise isgenerated between the crimped portion 213 of the hub wheel 210 of thebearing section 270 and the shoulder portion 261 of the outer jointmember 262.

The stick-slip noise means noise generated by abrupt sliding caused asfollows: upon starting of a vehicle, although rotational torque isapplied from the outer joint member 262 of the constant velocityuniversal joint 260 with respect to the hub wheel 210 of the bearingsection 270 in a static state so as to be transmitted from the outerjoint member 262 to the hub wheel 210 through intermediation of thefemale spline 211 and the male spline 268, the transmitted torquebetween the bearing section 270 and the outer joint member 262 variesand the outer joint member 262 twists, with the result that abruptsliding occurs between the crimped portion 213 of the hub wheel 210 andthe shoulder portion 261 of the outer joint member 262.

As means for preventing the stick-slip noise, there has been providedmeans for sandwiching a plate excellent in sliding properties betweenthe opposite surfaces of an inboard-side end portion of the bearingsection 270 and the shoulder portion 261 of the outer joint member 262(refer to Patent Literatures 1 and 2, for example).

In Patent Literatures 1 and 2 mentioned above, the plate is interposedbetween the opposite surfaces of the inboard-side end portion of thebearing section 270 and the shoulder portion 261 of the outer jointmember 262. As a result, frictional resistance is reduced between theopposite surfaces of the inboard-side end portion of the bearing section270 and the shoulder portion 261 of the outer joint member 262 so thatpositive sliding is caused. Thus, abrupt sliding is not caused, andhence generation of stick-slip noise is prevented.

Citation List

-   Patent Literature 1: JP 2003-97588 A-   Patent Literature 2: JP 2007-508986 A

SUMMARY OF INVENTION Technical Problems

Incidentally, the bearing devices disclosed in Patent Literatures 1 and2, as described above, an annular plate excellent in sliding propertiesis interposed between the opposite surfaces of the inboard-side endportion of the bearing section 270 and the shoulder portion 261 of theouter joint member 262. In this manner, generation of stick-slip noiseis prevented.

However, in those bearing devices, the constant velocity universal joint260 is fixed to the hub wheel 210 by an axial force exerted bytightening of the nut 272 to the male-screw portion 265 formed at theend portion of the stem section 266. Thus, owing to deformation and thelike of the plate with high surface pressure applied to the plate by theaxial force, there is a risk that the axial force is reduced. When theaxial force is reduced in this way, a gap is formed between the oppositesurfaces of the inboard-side end portion of the bearing section 270 andthe shoulder portion 261 of the outer joint member 262. In this context,when corrosion-resistance properties of the plate itself are low, antistick-slip properties of the plate is impaired owing to corrosion. As aresult, the thickness of the plate is reduced owing to the corrosion,which may lead to a risk of further reduction of the axial force. Inparticular, in a case of a type that the inboard-side end portion of thebearing section is not crimped outward (type that the inner race of thebearing section and the shoulder portion of the constant velocityuniversal joint are held in direct contact with each other), thereoccurs a failure of impairing durability of the bearing section.

Further, the surface roughness of the plate prior to coating is notdisclosed at all in any of Patent Literatures 1 and 2 described above.Thus, the applicants of the present invention have focused attention onthe surface roughness of the plate prior to coating.

In other words, when the surface roughness of the plate prior to coatingis excessively small, adhesion properties between the surface of theplate and a coating material are reduced. Thus, when rotational torqueis input in a state in which the plate is interposed between the bearingsection 270 and the shoulder portion 261 of the outer joint member 262,the coating material is caused to be peeled off early, and hence it hasbeen difficult to sufficiently yield the functions of the coatingmaterial. In contrast, when the surface roughness prior to coating isexcessively large, surface pressure of protruding portions becomeshigher with the surface roughness, and hence problems such as earlywearing of the coating material occur on that portions. Also in thiscase, it has been difficult to sufficiently yield the functions of thecoating material.

It is therefore an object of the present invention to provide adriving-wheel bearing device preventing reduction of the axial forceover a long period of time and being capable of securing anti stick-slipproperties.

Solution to Problems

In order to achieve the above-mentioned object, according to the presentinvention, there is provided a driving-wheel bearing device including:an outer member having double-row outer raceway surfaces formed on aninner periphery thereof; an inner member constituted by a hub wheel andan inner race, the inner member having a wheel attachment flange at oneend thereof and double-row inner raceway surfaces on an outer peripherythereof; and double-row rolling elements interposed between thedouble-row outer raceway surfaces of the outer member and the double-rowinner raceway surfaces of the inner member, the hub wheel having a shafthole into which a stem section extending from an outer joint member of aconstant velocity universal joint is spline-fitted by beingpress-fitted, in which a plate having a molybdenum coating layer or afluorine-resin coating layer formed thereon and having a plate thicknessranging from 0.5 mm to 2 mm is interposed between opposite surfaces of ashoulder portion of the outer joint member and an end portion of theinner member.

In the present invention, the plate endowed with excellent slidingproperties due to formation of the molybdenum coating layer or thefluorine-resin coating layer is interposed between the opposite surfacesof the shoulder portion of the outer joint member and the end portion ofthe inner member. As a result, even when transmitted torque between thebearing section having the inner member and the outer joint membervaries and the outer joint member twists, frictional resistance isreduced between the bearing section and the outer joint member so thatpositive sliding is caused. Thus, abrupt sliding is not caused betweenthe bearing section and the outer joint member, and hence generation ofstick-slip noise is prevented.

Further, when the thickness of the plate excellent in sliding propertiesis set to 0.5 mm or more, the strength of the plate is secured. Highsurface-pressure applied by the axial force to the plate preventsdeformation or the like of the plate, and hence reduction of the axialforce is prevented. Meanwhile, when the thickness of the plate is set to2 mm or less, compact design can be secured without increase in axialdimension of the bearing device.

It is desirable that a film thickness of the molybdenum coating layer orthe fluorine-resin coating layer of the present invention be set withina range from 2 μm to 30 μm. When the film thickness of the molybdenumcoating layer or the fluorine-resin coating layer is set to 2 μm ormore, the molybdenum coating layer or the fluorine-resin coating layeris not worn early. Further, when the film thickness of the molybdenumcoating layer or the fluorine-resin coating layer is set to 30 μm orless, use amount of a coating material is minimized, and hence costincrease is not involved. In addition, crush of the coating layer issuppressed even when high surface-pressure is applied by the axial forceto the plate, and hence reduction of the axial force is prevented, andhence durability of the bearing section can be secured.

It is desirable that the material of the plate of the present inventionbe stainless steel. With this configuration, the plate itself can becaused to yield corrosion-resistance effect, and hence generation ofstain is prevented. As a result, it is capable of coping with useenvironment in which corrosion-resistance properties such as those ofautomobiles are required over a long period of time.

It is desirable that a yield strength of the plate of the presentinvention be set to 205 N/mm² or more. With this setting, deformation ofthe plate is prevented even when high surface-pressure is applied by theaxial force to the plate, and hence reduction of the axial force isprevented.

It is desirable that the plate of the present invention be constitutedby an annular portion interposed between the two opposite surfaces ofthe shoulder portion of the outer joint member and the end portion ofthe inner member and by a cylindrical portion formed of a peripheraledge of the annular portion, the peripheral edge being elongated in anaxial direction and fitted to the shoulder portion of the outer jointmember. With this structure, when the cylindrical portion of the plateis fitted to the shoulder portion of the outer joint member, the platecan be interposed in a state in which the annular portion is easilypositioned between the two opposite surfaces of the end portion of theinner member and the shoulder portion of the outer joint member in astate in which the plate is assembled to the outer joint member.

Further, it is desirable that the plate of the present invention beconstituted by an annular portion interposed between the two oppositesurfaces of the shoulder portion of the outer joint member and the endportion of the inner member and by a cylindrical portion formed of aperipheral edge of the annular portion, the peripheral edge beingelongated in the axial direction and fitted to the end portion of theinner member. With this structure, when the cylindrical portion of theplate is fitted to the end portion of the inner member, the plate can beinterposed in a state in which the annular portion is easily positionedbetween the two opposite surfaces of the end portion of the inner memberand the shoulder portion of the outer joint member in a state in whichthe plate is assembled to the inner member.

Further, a driving-wheel bearing device according to the presentinvention includes: an outer member having double-row outer racewaysurfaces formed on an inner periphery thereof; an inner memberconstituted by a hub wheel and an inner race, the inner member having awheel attachment flange at one end thereof and double-row inner racewaysurfaces on an outer periphery thereof; and double-row rolling elementsinterposed between the double-row outer raceway surfaces of the outermember and the double-row inner raceway surfaces of the inner member,the hub wheel having a shaft hole into which a stem section extendingfrom an outer joint member of a constant velocity universal joint isspline-fitted by being press-fitted, in which: a plate endowed withpredetermined sliding properties by coating of at least one surface of asubstrate is interposed between opposite surfaces of a shoulder portionof the outer joint member and an end portion of the inner member; and asurface roughness of the coating-object substrate is set to beRz=0.2˜15.0. Note that, Rz means one of surface parameters defined inJIS, specifically, ten-point average roughness.

In this context, the description “at least one surface of a substrate”encompasses the following cases: coating only the substrate surfaceopposite to the shoulder portion of the outer joint member; coating onlythe substrate surface opposite to the end portion of the inner member;and coating both the substrate surfaces.

In the present invention, the plate endowed with predetermined slidingproperties due to coating of the surface of the substrate is interposedbetween the opposite surfaces of the shoulder portion of the outer jointmember and the end portion of the inner member. As a result, even whentransmitted torque between the bearing section having the inner memberand the outer joint member varies and the outer joint member twists,frictional resistance is reduced between the bearing section and theouter joint member so that positive sliding is caused. Thus, abruptsliding is not caused between the bearing section and the outer jointmember, and hence generation of stick-slip noise is prevented.

By setting of the surface roughness of the coating-object substrate ofthe plate to be Rz=0.2˜15.0, a coating material is more easily appliedonto the surfaces of the substrate, and hence adhesion properties areenhanced. As a result, even when rotational torque is input, problemssuch as early peeling-off and early wearing of the coating material areprevented, and hence functions of the coating material is sufficientlyyielded more easily.

In the present invention, it is desirable that a recess groove intowhich an inner periphery of the plate is fitted be formed on theshoulder portion of the outer joint member. When the recess groove intowhich the inner periphery of the plate is fitted is provided to theshoulder portion of the outer joint member, the plate can be easilyassembled to the shoulder portion of the outer joint member, and easilypositioned and interposed between the end portion of the inner wheel andthe shoulder portion of the outer joint member in a state in which theplate is assembled to the outer joint member.

It should be noted that it is desirable that an escape portion beprovided at an innermost part of the recess groove into which the plateis fitted. When the escape portion is provided as just described above,the fitting work is facilitated when the plate is fitted into the recessgroove of the shoulder portion of the outer joint member.

In the present invention, it is desirable that claw-like protrusions beprovided on the inner periphery of the plate. With this structure,mountability of the plate is enhanced. In other words, with provision ofthe claw-like protrusions, for example, at a plurality of points alongthe circumferential direction of the inner periphery of the plate, onlythe parts corresponding to the protrusions come into contact with theshoulder portion of the outer joint member in the circumferentialdirection of the inner periphery of the plate, and hence the plate ismore easily mounted to the outer joint member.

It is desirable that the plate of the present invention be endowed withthe predetermined sliding properties by being subjected to coating witha film containing at least one of a fluorine resin and molybdenumdisulfide. In order to easily secure the predetermined slidingproperties of the plate, it is only necessary that the plate besubjected to coating with the film containing at least one of a fluorineresin and molybdenum disulfide.

In this context, the description “the film containing at least one of afluorine resin and molybdenum disulfide” encompasses the followingcases: coating only with the film containing a fluorine resin; coatingonly with the film containing molybdenum disulfide; and coating with thefilm containing both a fluorine resin and molybdenum disulfide.

In the present invention, it is desirable that lubricant be interposedin at least one of a gap between the plate and the shoulder portion ofthe outer joint member and a gap between the plate and the end portionof the inner member. With this structure, the frictional resistance isfurther reduced between the bearing section and the outer joint memberso that positive sliding easily occurs, with the result that generationof stick-slip noise is more reliably prevented.

In this context, the description “at least one of a gap between theplate and the shoulder portion of the outer joint member and a gapbetween the plate and the end portion of the inner member” encompassesthe following cases: interposing lubricant only in the gap between theplate and the shoulder portion of the outer joint member; interposinglubricant only in the gap between the plate and the end portion of theinner member; and interposing lubricant in both the gaps.

Note that, the bearing device is applicable to a bearing device of thefollowing type: the small-diameter step portion is formed on the outerperipheral surface of the hub wheel, the one-side inner raceway surfacebeing formed on the outer peripheral surface; the inner race providedwith the other-side inner raceway surface is press-fitted to thesmall-diameter step portion; and the end portion of the small-diameterstep portion of the hub wheel is crimped. In this case, the crimpedportion of the hub wheel is opposed to the shoulder portion of the outerjoint member.

Further, other than the bearing device of the type described above, thebearing device is also applicable to a bearing device of the followingtype: the pair of inner races are fitted to the outer peripheral surfaceof the hub wheel; the outboard-side inner raceway surface is formed onthe outer peripheral surface of the one-side inner race; and theinboard-side inner raceway surface is formed on the outer peripheralsurface of the other-side inner race. In this case, an end portion ofthe other-side inner race positioned on the inboard-side is opposed tothe shoulder portion of the outer joint member.

Advantageous Effects of Invention

According to the present invention, upon starting of a vehicle, in acase where rotational torque is applied from the outer joint member ofthe constant velocity universal joint with respect to the hub wheel ofthe bearing section in a static state, even when the transmitted torquebetween the bearing section having the inner member and the outer jointmember varies and the outer joint member twists, frictional resistanceis reduced between the bearing section and the outer joint member sothat positive sliding is caused. Thus, abrupt sliding is not causedbetween the bearing section and the outer joint member. As a result,generation of stick-slip noise is prevented, and hence it is possible toenhance quietness and to eliminate unpleasant feeling of drivers.

Further, when the thickness of the plate excellent in sliding propertiesis set to 0.5 mm to 2 mm, the following advantages can be obtained: thestrength of the plate is secured; high surface-pressure applied by theaxial force to the plate prevents deformation or the like of the plate,and hence reduction of the axial force is prevented over a long periodof time; and anti stick-slip properties are secured. As a result, it ispossible to provide a compact driving-wheel bearing device.

In addition, by setting of the surface roughness of the coating-objectsubstrate to be Rz=0.2˜15.0, a coating material is more easily appliedonto the surfaces of the substrate, and hence adhesion properties areenhanced. As a result, even when rotational torque is input, problemssuch as early peeling-off and early wearing of the coating material areprevented, and hence functions of the coating material is sufficientlyyielded more easily. Consequently, it is possible to provide adriving-wheel bearing device endowed with anti stick-slip propertiessecured over a long period of time.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A vertical sectional view illustrating an application exampleof a first embodiment of the present invention, in which a plate isinterposed between a crimped portion of a hub wheel and a shoulderportion of an outer joint member.

[FIG. 2] A vertical sectional view illustrating an application exampleof a second embodiment of the present invention, in which the plate isinterposed between an inboard-side end portion of an inner race and theshoulder portion of the outer joint member.

[FIG. 3] A vertical sectional view illustrating an application exampleof a third embodiment of the present invention, in which a plateassembled to the outer joint member is interposed between the crimpedportion of the hub wheel and the shoulder portion of the outer jointmember.

[FIG. 4] A vertical sectional view illustrating an application exampleof a fourth embodiment of the present invention, in which the plateassembled to the outer joint member is interposed between theinboard-side endportion of the inner race and the shoulder portion ofthe outer joint member.

[FIG. 5] A vertical sectional view illustrating an application exampleof a fifth embodiment of the present invention, in which a plateassembled to a bearing section is interposed between the crimped portionof the hub wheel and the shoulder portion of the outer joint member.

[FIG. 6] A vertical sectional view illustrating an application exampleof a sixth embodiment of the present invention, in which a plateassembled to the bearing section is interposed between the inboard-sideendportion of the inner race and the shoulder portion of the outer jointmember.

[FIG. 7] A vertical sectional view illustrating an application exampleof a seventh embodiment of the present invention, in which a plate isinterposed between the crimped portion of the hub wheel and the shoulderportion of the outer joint member.

[FIG. 8A] A partially enlarged sectional view of the plate of FIG. 7.

[FIG. 8B] A partially enlarged front view of the shoulder portion of theouter joint member of FIG. 7.

[FIG. 9] A side view of the plate having a radially-inner circularshape.

[FIG. 10] A partially enlarged view of a state in which the plate ofFIG. 9 is assembled to the shoulder portion of the outer joint member.

[FIG. 11] A vertical sectional view illustrating an application exampleof an eighth embodiment of the present invention, in which the plate isinterposed between the inboard-side end portion of the inner race andthe shoulder portion of the outer joint member.

[FIG. 12] A vertical sectional view illustrating an application exampleof a ninth embodiment of the present invention, in which a plate isinterposed between the crimped portion of the hub wheel and the shoulderportion of the outer joint member.

[FIG. 13] A vertical sectional view illustrating an application exampleof a tenth embodiment of the present invention, in which the plate isinterposed between the inboard-side end portion of the inner race andthe shoulder portion of the outer joint member.

[FIG. 14] A side view of the plate having protrusions provided on aninner periphery thereof.

[FIG. 15] A partially enlarged view of a state in which the plate ofFIG. 14 is assembled to the shoulder portion of the outer joint member.

[FIG. 16] A vertical sectional view illustrating a conventional exampleof a driving-wheel bearing device.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of a driving-wheel bearing deviceaccording to the present invention are described in detail. Adriving-wheel bearing device according to a first embodiment illustratedin FIG. 1 includes the following as main components: a hub wheel 10 andinner race 20 which serve as inner members; double-row rolling elements30 and 40; an outer race 50 which serves as an outer member; and aconstant velocity universal joint 60. Note that, in the followingdescription, an outer side of a vehicle in a state in which the bearingdevice is assembled to the vehicle is referred to as an outboard side(left side in the figures), and a middle side of the vehicle is referredto as an inboard side (right side in the figures).

The hub wheel 10 has an outboard-side inner raceway surface 12 formed onan outer peripheral surface thereof, and includes a wheel attachmentflange 14 for allowing a wheel (not shown) to be attached thereto. Hubbolts 16 for fixing a wheel disk are equiangularly embedded in the wheelattachment flange 14. The inner race 20 is fitted to a small-diameterstep portion 18 formed on the outer peripheral surface of the hub wheel10, and an inboard-side inner raceway surface 22 is formed on an outerperipheral surface of the inner race 20. A female spline 11 for couplingthe constant velocity universal joint 60 with the hub wheel 10 so thattorque can be transmitted therebetween is formed on an inner peripheralsurface of a shaft hole of the hub wheel 10.

The inner race 20 is press-fitted to the small-diameter step portion 18of the hub wheel 10 with adequate tightening margin for the purpose ofpreventing creep. The outboard-side inner raceway surface 12 formed onthe outer peripheral surface of the hub wheel 10 and the inboard-sideinner raceway surface 22 formed on the outer peripheral surface of theinner race 20 constitute double-row inner raceway surfaces. The innerrace 20 is press-fitted to the small-diameter step portion 18 of the hubwheel 10, and the end portion of the small-diameter step portion 18 ofthe hub wheel 10 is crimped outward. As a result, the inner race 20 isprevented from slipping off by a crimped portion 13 thus formed, and isintegrated with the hub wheel 10, to thereby apply preload to a bearingsection 70.

The outer race 50 has double-row outer raceway surfaces 52 and 54 formedon an inner peripheral surface thereof and opposed to the inner racewaysurfaces 12 and 22 of the hub wheel 10 and the inner race 20, andincludes a vehicle body attachment flange 56 for being attached to avehicle body (not shown). The vehicle body attachment flange 56 isfixed, with use of an attachment hole 58, by bolts or the like to aknuckle extending from a suspension device (not shown) of a vehiclebody.

The bearing section 70 has a double-row angular ball bearing structure,specifically, has the following structure: the rolling elements 30 and40 are interposed between the inner raceway surfaces 12 and 22 formed onthe outer peripheral surfaces of the hub wheel 10 and inner race 20 andthe outer raceway surfaces 52 and 54 formed on the inner peripheralsurface of the outer race 50, the rolling elements 30 and 40 inrespective rows being rotatably and equiangularly retained by retainers32 and 42.

At the openings on both ends of the bearing section 70, a pair of seals34 and 44 for sealing annular spaces between the outer race 50 and thehub wheel 10 and between the outer race 50 and the inner race 20 so asto be held in sliding-contact with the outer peripheral surfaces of thehub wheel 10 and inner race 20 are fitted to the inner periphery at bothend portions of the outer race 50. Further, the seals 34 and 44 preventleakage of grease filling the inside and intrusion of water and foreignmatters from the outside.

An outer joint member 62 of the constant velocity universal joint 60 iscoupled with the hub wheel 10 described above, and hence a bearingdevice is constituted. The outer joint member 62 of the constantvelocity universal joint 60 is provided at one end of an intermediateshaft (not shown) constituting a drive shaft, and is constituted by thefollowing: a cup-shaped mouth section 64 housing inner components (notshown) including an inner joint member, balls, and a cage; and a stemsection 66 extending integrally from a proximal portion of the mouthsection 64 in an axial direction. A male spline 68 for coupling the hubwheel 10 described above with the constant velocity universal joint 60so that torque can be transmitted therebetween is formed on an outerperipheral surface of the stem section 66.

The stem section 66 of the outer joint member 62 is press-fitted to theshaft hole of the hub wheel 10, and the male spline 68 formed on theouter peripheral surface of the stem section 66 and the female spline 11formed on the inner peripheral surface of the shaft hole of the hubwheel 10 are fitted to each other. In this manner, torque can betransmitted. In the bearing device according to this embodiment, anannular plate 80 excellent in sliding properties is interposed betweenopposite surfaces of a shoulder portion 61 of the outer joint member 62and the crimped portion 13 of the hub wheel 10, and a nut 72 istightened to a male-screw portion 65 formed at an end portion of thestem section 66. In this manner, the constant velocity universal joint60 is fixed to the hub wheel 10. Note that, the constant velocityuniversal joint 60 and the hub wheel 10 may be fixed to each other witha bolt other than the nut 72.

By a predetermined tightening force (axial force) of the nut 72, theplate 80 is sandwiched between the opposite surfaces of the shoulderportion 61 of the outer joint member 62 and the crimped portion 13 ofthe hub wheel 10. The plate 80 interposed between the opposite surfacesof the shoulder portion 61 of the outer joint member 62 and the crimpedportion 13 of the hub wheel is provided with a molybdenum (MoS₂) coatinglayer or a fluorine-resin coating layer 81 and has a plate thicknessranging from 0.5 mm to 2 mm. Note that, the thickness of the plate 80preferably ranges from 0.8 mm to 1 mm.

As described above, the plate 80 endowed with excellent slidingproperties due to formation of the molybdenum coating layer or thefluorine-resin coating layer 81 is interposed between the oppositesurfaces of the shoulder portion 61 of the outer joint member 62 and thecrimped portion 13 of the hub wheel 10. As a result, even whentransmitted torque between the bearing section 70 and the outer jointmember 62 varies and the outer joint member 62 twists, frictionalresistance is reduced between the bearing section 70 and the outer jointmember 62 so that positive sliding is caused. Thus, abrupt sliding isnot caused between the bearing section 70 and the outer joint member 62,and hence generation of stick-slip noise is prevented.

Further, when the thickness of the plate 80 excellent in slidingproperties is set to 0.5 mm or more, the strength of the plate 80 issecured. High surface-pressure applied by the axial force to the plate80 prevents deformation or the like of the plate 80, and hence reductionof the axial force is prevented over a long period of time. Antistick-slip properties are secured in this manner. Meanwhile, when thethickness of the plate 80 is set to 2 mm or less, compact design can besecured without increase in axial dimension of the bearing device.

When the thickness of the plate 80 is less than 0.5 mm, it is difficultto secure the strength of the plate 80, which may lead to such a riskthat the plate 80 is liable to be deformed in a case of being appliedwith high surface-pressure by the axial force, and that the axial forceis reduced, which may cause a breakage of the plate 80. Further, whenthe thickness of the plate 80 is more than 2 mm, the axial dimension ofthe bearing device is increased, which leads to difficulty incompactification of the device.

The film thickness of the molybdenum coating layer or the fluorine-resincoating layer 81 formed on the plate 80 is set within a range from 2 μmto 30 μm. When the film thickness of the molybdenum coating layer or thefluorine-resin coating layer 81 is set to 2 μm or more, the molybdenumcoating layer or the fluorine-resin coating layer 81 is not worn early.Further, when the film thickness of the molybdenum coating layer or thefluorine-resin coating layer 81 is set to 30 μm or less, use amount of acoating material is minimized, and hence cost increase is not involved.In addition, the coating layer 81 itself is not crushed even when highsurface-pressure is applied by the axial force to the plate 80, andhence reduction of the axial force is prevented, and hence the nut 72 isprevented from being loosened.

When the film thickness of the coating layer 81 is less than 2 μm, thereis a risk that the coating layer 81 is worn early. Further, when thefilm thickness of the coating layer 81 is more than 30 μm, use amount ofa coating material is increased, which leads to cost increase. Inaddition, the coating layer 81 itself is crushed when highsurface-pressure is applied by the axial force to the plate 80, whichleads to reduction of the axial force and formation of a gap between theopposite surfaces of an inboard-side end portion of the bearing sectionand the shoulder portion of the outer joint member. When the wheelbearing device is of a type that the inboard-side end portion of thebearing section is not crimped outward (type that the inner race of thebearing section and the shoulder portion of the constant velocityuniversal joint are held in direct contact with each other), thereoccurs a failure of impairing durability of the bearing section.

The material of the plate 80 is stainless steel. When the plate 80 isformed of stainless steel as just described above, the plate 80 itselfcan be caused to yield corrosion-resistance effect. As a result,generation of stain is prevented, and hence use environment can also becoped with in which corrosion-resistance properties such as those ofautomobiles are required over a long period of time.

Further, the yield strength of the plate 80 is set to 205 N/mm² or more.When the yield strength of the plate 80 is set to 205 N/mm² or more asjust described above, deformation of the plate 80 is prevented even whenhigh surface-pressure is applied by the axial force to the plate 80, andhence reduction of the axial force is prevented.

In the first embodiment described above, the case is described where thepresent invention is applied to a bearing device of the following type:the small-diameter step portion 18 is formed on the outer peripheralsurface of the hub wheel 10, the one-side inner raceway surface 12 beingformed on the outer peripheral surface; the inner race 20 provided withthe other-side inner raceway surface 22 is press-fitted to thesmall-diameter step portion 18; and the end portion of thesmall-diameter step portion 18 of the hub wheel 10 is crimped. However,the present invention is not limited thereto.

For example, as illustrated in FIG. 2, the present invention isapplicable to a bearing device of the following type: a pair of innerraces 20 a and 20 b are fitted to the outer peripheral surface of thehub wheel 10; an outboard-side inner raceway surface 22 a is formed onan outer peripheral surface of the one-side inner race 20 a; and aninboard-side inner raceway surface 22 b is formed on an outer peripheralsurface of the other-side inner race 20 b.

In a second embodiment of the present invention illustrated in FIG. 2,an inboard-side end portion of the other-side inner race 20 b positionedon an inboard side is opposed to the shoulder portion 61 of the outerjoint member 62. Thus, the plate 80 described in the first embodiment isinterposed between the inboard-side end portion of the inner race 20 band the shoulder portion 61 of the outer joint member 62. Note that, theplate 80 is similar to that described above in the first embodiment inconstitution, that is, in the following points: the molybdenum coatinglayer or the fluorine-resin coating layer 81 is formed thereon and theplate 80 has a plate thickness ranging from 0.5 mm to 2 mm; the filmthickness of the molybdenum coating layer or the fluorine-resin coatinglayer 81 is set within a range from 2 μm to 30 μm; the material of theplate 80 is stainless steel; and the yield strength of the plate 80 isset to 205 N/mm² or more, and in functions and advantages. Therefore,redundant description thereof is omitted. In the second embodiment, theplate 80 also has an advantage of preventing durability of the bearingsection 70 from being reduced owing to reduction of the axial force.

Further, in the first embodiment illustrated in FIG. 1 and the secondembodiment illustrated in FIG. 2, the case is described where theannular plate 80 is used. However, as in a third embodiment of thepresent invention illustrated in FIG. 3 and a fourth embodiment of thepresent invention illustrated in FIG. 4, a plate 82 maybe used which hasan annular portion 82 a and a cylindrical portion 82 b. In the thirdembodiment illustrated in FIG. 3, similar to the first embodiment, thepresent invention is applied to a bearing device of a type that the endportion of the small-diameter step portion 18 of the hub wheel 10 iscrimped; in the fourth embodiment illustrated in FIG. 4, similar to thesecond embodiment, the present invention is applied to a bearing deviceof a type that the pair of inner races 20 a and 20 b are fitted to theouter peripheral surface of the hub wheel 10.

The plate 82 according to the third embodiment has a structureconstituted by the following: the annular portion 82 a interposedbetween the two opposite surfaces of the shoulder portion 61 of theouter joint member 62 and the crimped portion 13 of the hub wheel 10;and the cylindrical portion 82 b formed of an outer peripheral edge ofthe annular portion 82 a, the outer peripheral edge being elongated toan axial inboard side and fitted to the shoulder portion 61 of the outerjoint member 62. Similarly, the plate 82 according to the fourthembodiment has a structure constituted by the following: the annularportion 82 a interposed between the two opposite surfaces of theshoulder portion 61 of the outer joint member 62 and the inboard-sideend portion of the inner race 20 b; and the cylindrical portion 82 bformed of an outer peripheral edge of the annular portion 82 a, theouter peripheral edge being elongated to an axial inboard side andfitted to the shoulder portion 61 of the outer joint member 62.

Each of the plates 82 is provided with a molybdenum coating layer or afluorine-resin coating layer 83 and has a plate thickness ranging from0.5 mm to 2 mm. Further, the film thickness of the molybdenum coatinglayer or the fluorine-resin coating layer 83 formed on each of theplates 82 is set within a range from 2 μm to 30 μm. In addition, thematerial of the plates 82 is stainless steel, and the yield strengththereof is set to 205 N/mm² or more. Functions and advantages yielded bythe annular portion 82 a of each of the plates 82 constituted asdescribed above are similar to those of the annular plates 80 in thefirst embodiment illustrated in FIG. 1 and the second embodimentillustrated in FIG. 2, and hence redundant description thereof isomitted.

With use of the plates 82 structured as described above, each of theplate 82 can be assembled to the outer joint member 62 by fitting of thecylindrical portion 82 b of each of the plates 82 to the shoulderportion 61 of the outer joint member 62. As a result, the plates 82 canbe handled more easily. Further, in the case of the third embodiment,the annular portion 82 a of the plate 82 can be easily positionedbetween the opposite surfaces of the crimped portion 13 of the hub wheel10 and the shoulder portion 61 of the outer joint member 62; in the caseof the fourth embodiment, the annular portion 82 a of the plate 82 canbe easily positioned between the opposite surfaces of the inboard-sideend portion of the inner race 20 b and the shoulder portion 61 of theouter joint member 62.

In the third embodiment illustrated in FIG. 3 and the fourth embodimentillustrated in FIG. 4, the case is described where each of the plates 82has a structure in which an outer peripheral edge of the annular portion82 a is elongated to the axial inboard side and the cylindrical portion82 b is fitted to the shoulder portion 61 of the outer joint member 62,and hence each of the plates 82 can be assembled to the outer jointmember 62. However, the present invention is not limited thereto, and itis also possible to use plates 84 and 86 which respectively havestructures in a fifth embodiment of the present invention illustrated inFIG. 5 and a sixth embodiment of the present invention illustrated inFIG. 6.

Note that, in the fifth embodiment illustrated in FIG. 5 is, similar tothe third embodiment, the present invention is applied to a bearingdevice of a type that the end portion of the small-diameter step portion18 of the hub wheel 10 is crimped; in the sixth embodiment illustratedin FIG. 6, similar to the fourth embodiment, the present invention isapplied to a bearing device of a type that the pair of inner races 20 aand 20 b are fitted to the outer peripheral surface of the hub wheel 10.

The plate 84 according to the fifth embodiment has a structureconstituted by the following: an annular portion 84 a interposed betweenthe two opposite surfaces of the shoulder portion 61 of the outer jointmember 62 and the crimped portion 13 of the hub wheel 10; and acylindrical portion 84 b formed of an outer peripheral edge of theannular portion 84 a, the outer peripheral edge being elongated to anaxial outboard side and fitted to the inboard-side end portion of theinner race 20. Meanwhile, the plate 86 according to the sixth embodimenthas a structure constituted by the following: the annular portion 84 ainterposed between the two opposite surfaces of the shoulder portion 61of the outer joint member 62 and the inboard-side end portion of theinner race 20 b; and a cylindrical portion 86 b formed of an innerperipheral edge of the annular portion 84 a, the outer peripheral edgebeing elongated to the axial outboard side and fitted to theinboard-side end portion of the inner race 20 b.

The plates 84 and 86 are provided with molybdenum coating layers orfluorine-resin coating layers 85 and 87, respectively, and each has aplate thickness ranging from 0.5 mm to 2 mm. Further, the film thicknessof the molybdenum coating layer or the respective fluorine-resin coatinglayers 85 and 87 formed on the plates 84 and 86 is set within a rangefrom 2 μm to 30 μm. In addition, the material of the plates 84 and 86 isstainless steel, and the yield strength thereof is set to 205 N/mm² ormore. Functions and advantages yielded by the respective annular portion84 a and 86 a of the plates 84 and 86 constituted as described above aresimilar to those of the annular plates 80 in the first embodimentillustrated in FIG. 1 and the second embodiment illustrated in FIG. 2,and hence redundant description thereof is omitted.

With use of the plates 84 and 86, the plates 84 and 86 can be assembledto the bearing section 70 by fitting of the cylindrical portion 84 b ofthe plate 84 to the crimped portion 13 of the hub wheel 10 in the caseof the fifth embodiment, and by fitting of the cylindrical portion 86 bof the plate 86 to the inboard-side end portion of the inner race 20 bin the case of the sixth embodiment. As a result, the plates 84 and 86can be handled more easily. Further, in the case of the fifthembodiment, the annular portion 84 a of the plate 84 can be easilypositioned between the opposite surfaces of the crimped portion 13 ofthe hub wheel 10 and the shoulder portion 61 of the outer joint member62; in the case of the sixth embodiment, the annular portion 86 b of theplate 86 can be easily positioned between the opposite surfaces of theinboard-side end portion of the inner race 20 b and the shoulder portion61 of the outer joint member 62.

In a seventh embodiment of the present invention illustrated in FIG. 7,a plate 180 is sandwiched by a predetermined tightening force (axialforce) of the nut 72 between the opposite surfaces of the shoulderportion 61 of the outer joint member 62 and the crimped portion 13 ofthe hub wheel 10. The plate 180 interposed between the opposite surfacesof the shoulder portion 61 of the outer joint member 62 and the crimpedportion 13 of the hub wheel 10 is endowed with predetermined slidingproperties by coating of surfaces of a substrate 181 thereof with a film182 containing a fluorine resin or molybdenum disulfide. Further, thesurface roughness of the plate 180 prior to coating, that is, thesurface roughness of the coating-object substrate 181 is set to beRz=0.2˜15.0. The surface roughness of the plate 180 prior to coating ispreferably set to be Rz=0.3˜10.0.

Note that, in the seventh embodiment, although a case is illustratedwhere both an outer-joint-member-side surface and hub-wheel-side surfaceof the substrate 181 are subjected to coating, only theouter-joint-member-side surface of the substrate 181 may be subjected tocoating, or only the hub-wheel-side surface of the substrate 181 may besubjected to coating. The surface roughness (Rz=0.2˜15.0) describedabove is set for the coating-object surfaces of the substrate 181.

Further, in order to secure excellent sliding properties, the plate 180is subjected to coating with the film 182 containing a fluorine resin ormolybdenum disulfide. Any of the following cases may be applied: a caseof effecting coating with the film 182 containing only a fluorine resin;a case of effecting coating with the film 182 containing only molybdenumdisulfide; and a case of effecting coating with a film 182 containingboth a fluorine resin and molybdenum disulfide.

As described above, the plate 180 endowed with excellent slidingproperties due to coating of the surfaces of the substrate 181 isinterposed between the opposite surfaces of the shoulder portion 61 ofthe outer joint member 62 and the crimped portion 13 of the hub wheel10. As a result, even when transmitted torque between the bearingsection 70 and the outer joint member 62 varies and the outer jointmember 62 twists, frictional resistance is reduced between the bearingsection 70 and the outer joint member 62 so that positive sliding iscaused. Thus, abrupt sliding is not caused between the bearing section70 and the outer joint member 62, and hence generation of stick-slipnoise is prevented.

By setting of the surface roughness of the coating-object substrate 181of the plate 180 to be Rz=0.2˜15.0, a coating material containing afluorine resin or molybdenum disulfide is more easily applied onto thesurfaces of the substrate 181, and hence adhesion properties of thecoating material with respect to the surfaces of the substrate 181 areenhanced. As a result, even when rotational torque is input, problemssuch as early peeling-off and early wearing of the coating material areprevented, and hence functions of the coating material is sufficientlyyielded more easily.

In this embodiment, the case is illustrated where both theouter-joint-member-side surface and hub-wheel-side surface of thesubstrate 181 are subjected to coating. In this context, although it isnecessary to set the surface roughness of both the surfaces of thesubstrate 181 to be Rz=0.2˜15.0, only the outer-joint-member-sidesurface of the substrate 181 may be subjected to coating. Alternatively,when only the hub-wheel-side surface of the substrate 181 is subjectedto coating, it is only necessary that the surface roughness of thecoating-object outer-joint-member-side surface or hub-wheel-side surfacebe set to be Rz=0.2˜15.0.

When the surface roughness of the coating-object substrate 181 is lessthan Rz=0.2, adhesion properties between the surfaces of the substrate181 and the coating material are reduced. Thus, when rotational torqueis input in a state in which the plate 180 is interposed between thebearing section 70 and the shoulder portion 61 of the outer joint member62, the coating material is caused to be peeled off early, and hence itis difficult to sufficiently yield the functions of the coatingmaterial. In contrast, when the surface roughness of the coating-objectsubstrate 181 is more than Rz=15.0, surface pressure of protrudingportions on the surface thereof becomes higher, and hence problems suchas early wearing of the coating material occur on that portions. Also inthis case, it is difficult to sufficiently yield the functions of thecoating material.

As illustrated in FIGS. 8B and 10, a recess groove 90 into which aninner periphery of the plate 180 is fitted is formed on the shoulderportion 61 of the outer joint member 62 with which the plate 180illustrated in FIGS. 8A and 9 comes into contact, and an escape portion91 is provided at an innermost part of the recess groove 90 into whichthe plate 180 is fitted. Note that, the recess groove 90 has alarge-diameter inlet portion 90 a through which the plate 180 isinserted and a small-diameter groove-bottom portion 90 b into which theplate 180 is fitted.

As described above, the recess groove 90 into which the inner peripheryof the plate 180 is fitted is provided to the shoulder portion 61 of theouter joint member 62. With this configuration, the plate 180 can beeasily assembled to the shoulder portion 61 of the outer joint member62, and easily positioned and interposed between the crimped portion 13of the hub wheel 10 and the shoulder portion 61 of the outer jointmember 62 in a state in which the plate 180 is assembled to the outerjoint member 62. Further, the escape portion 91 is provided at theinnermost part of the recess groove 90. With this configuration, fittingwork is facilitated when the plate 180 is fitted into the recess groove90 of the shoulder portion 61 of the outer joint member 62.

In this context, when the inner diameter of the plate 180 is defined asd₁, the thickness thereof as t, the diameter of the inlet portion 90 aof the recess groove 90 of the outer joint member 62 as D₁, the diameterof the groove-bottom portion 90 b as D₂, and an axial length as L, thefollowing relations are established: D₂<d₁<D₁ and t<L. With thissetting, the plate 180 can be easily assembled to the shoulder portion61 of the outer joint member 62, and is not slipped off from the outerjoint member 62 at the time of handling or the like in the state inwhich the plate 180 is assembled to the outer joint member 62. As aresult, assembling properties and handling properties of the plate 180are enhanced. Note that, when the difference between the diameter D₁ ofthe inlet portion 90 a of the recess groove 90 and the inner diameter d₁of the plate 180 is defined as 0<D₁−d₁<0.5, the plate 180 can be easilyassembled to the extent of being attachable by hand.

In the seventh embodiment described above, the case is described wherethe present invention is applied to a bearing device of the followingtype: the small-diameter step portion 18 is formed on the outerperipheral surface of the hub wheel 10, the one-side inner racewaysurface 12 being formed on the outer peripheral surface; the inner race20 provided with the other-side inner raceway surface 22 is press-fittedto the small-diameter step portion 18; and the end portion of thesmall-diameter step portion 18 of the hub wheel 10 is crimped. However,the present invention is not limited thereto.

For example, as illustrated in FIG. 11, the present invention isapplicable to a bearing device of the following type: the pair of innerraces 20 a and 20 b are fitted to the outer peripheral surface of thehub wheel 10; the outboard-side inner raceway surface 22 a is formed onthe outer peripheral surface of the one-side inner race 20 a; and theinboard-side inner raceway surface 22 b is formed the outer peripheralsurface of the other-side inner race 20 b.

In an eighth embodiment of the present invention illustrated in FIG. 11,the inboard-side end portion of the other-side inner race 20 bpositioned on the inboard side is opposed to the shoulder portion 61 ofthe outer joint member 62. Thus, the plate 180 described in the seventhembodiment is interposed between the inboard-side end portion of theinner race 20 b and the shoulder portion 61 of the outer joint member62.

Note that, the plate 180 is similar to that described above in theseventh embodiment of the present invention in the following points: theplate 180 is endowed with predetermined sliding properties by coating ofthe surfaces of the substrate 181 thereof with the film 182 containing afluorine resin or molybdenum disulfide, and the surface roughness of thecoating-object substrate 181 of the plate 180 is preferably set to beRz=0.2˜15.0 (preferably, Rz=0.3˜10.0); the recess groove 90 and theescape portion 91 are provided to the shoulder portion 61 of the outerjoint member 62; the relations between the plate 180 and the recessgroove 90 are established as follows: D₂<d₁<D₁, t<L, and 0<D₁−d₁<0.5;and in functions and advantages. Therefore, redundant descriptionthereof is omitted.

In the seventh and eighth embodiments described above, a case isillustrated where the inner periphery of the plate 180 is formed in acircular shape (refer to FIG. 9). However, the present invention is notlimited thereto, and it is also possible to use a plate 184 as in aninth embodiment of the present invention illustrated in FIG. 12 and atenth embodiment of the present invention illustrated in FIG. 13.

Note that, in the ninth embodiment, similar to the seventh embodiment,the case is described where the present invention is applied to abearing device of a type that the inner race 20 is press-fitted to thesmall-diameter step portion 18 of the hub wheel 10 and then the endportion of the small-diameter step portion 18 of the hub wheel 10 iscrimped. In this case, the plate 184 is interposed between the crimpedportion 13 of the hub wheel 10 and the shoulder portion 61 of the outerjoint member 62.

Further, in the tenth embodiment, similar to the eighth embodiment, thecase is described where the present invention is applied to a bearingdevice of a type that the pair of inner races 20 a and 20 b are fittedto the outer peripheral surface of the hub wheel 10. In this case, theplate 184 is interposed between the inboard-side end portion of theinner race 20 b and the shoulder portion 61 of the outer joint member62.

The plate 184 is similar to that described above in the seventhembodiment of the present invention in the following points: the plate184 is endowed with predetermined sliding properties by coating ofsurfaces of a substrate 185 thereof with a film 186 containing afluorine resin or molybdenum disulfide, and the surface roughness of thecoating-object substrate 185 of the plate 184 is preferably set to beRz=0.2˜15.0 (preferably, Rz=0.3˜10.0); the recess groove 90 and theescape portion 91 are provided to the shoulder portion 61 of the outerjoint member 62; the relations between the plate 184 and the recessgroove 90 are established as follows: D₂<d₁<D₁, t<L, and 0<D₁−d₁<0.5;and in functions and advantages . Therefore, redundant descriptionthereof is omitted.

In the ninth and tenth embodiments, as illustrated in FIGS. 14 and 15,claw-like protrusions 187 are provided on an inner periphery of theplate 184. In those embodiments, three protrusions 187 are equiangularlyformed on the inner periphery of the plate 184. Note that, in therelations between the plate 184 and the recess groove 90, that is, inthe relations of D₂<d₁<D₁, t<L, and 0<D₁−d₁<0.5, the inner diameter d₁of the plate 184 is defined as an inner diameter measured from each ofthe portions corresponding to the protrusions 187 provided on the innerperiphery thereof.

With provision of the claw-like protrusions 187 on the inner peripheryof the plate 184 as in those ninth and tenth embodiments, mountabilityof the plate 184 is enhanced. In other words, with provision of theclaw-like protrusions 187, for example, at three points along thecircumferential direction of the inner periphery of the plate 184, onlythe parts corresponding to the protrusions 187 come into contact withthe shoulder portion 61 of the outer joint member 62 in thecircumferential direction of the inner periphery of the plate 184, andhence the plate 184 is more easily mounted to the outer joint member 62.Note that, an inner end portion of each of the protrusions 187 is formedin a shape of being bent to the crimped portion 13 of the hub wheel 10,and hence the plate 184 can be more easily fitted and less liable to bedisengaged.

In the seventh to tenth embodiments described above, lubricant may beinterposed in any one of a gap between each of the plate 180 and 184 andthe shoulder portion 61 of the outer joint member 62 and a gap betweeneach of the plate 180 and 184 and the crimped portion 13 of the hubwheel 10. Alternatively, lubricant may be interposed in both the gapbetween each of the plate 180 and 184 and the shoulder portion 61 of theouter joint member 62 and the gap between each of the plate 180 and 184and the crimped portion 13 of the hub wheel 10.

When the lubricant is interposed as described above, the frictionalresistance is further reduced between the bearing section 70 and theouter joint member 62 so that positive sliding easily occurs, with theresult that generation of stick-slip noise is more reliably prevented.

The present invention is not limited to the embodiments described above,and as a matter of course, may be carried out in other variousembodiments without departing from the spirit of the present invention.The scope of the present invention is defined in the scope of claims,and includes meaning of equivalents of elements described in the scopeof claims and all modifications in the scope of claims.

1. A driving-wheel bearing device, comprising: an outer member havingdouble-row outer raceway surfaces formed on an inner periphery thereof;an inner member constituted by a hub wheel and an inner race, the innermember having a wheel attachment flange at one end thereof anddouble-row inner raceway surfaces on an outer periphery thereof; anddouble-row rolling elements interposed between the double-row outerraceway surfaces of the outer member and the double-row inner racewaysurfaces of the inner member, the hub wheel having a shaft hole intowhich a stem section extending from an outer joint member of a constantvelocity universal joint is spline-fitted, wherein a plate having acoating layer which is formed thereon and is excellent in slidingproperties and having a plate thickness ranging from 0.5 mm to 2 mm isinterposed between opposite surfaces of a shoulder portion of the outerjoint member and an end portion of the inner member.
 2. A driving-wheelbearing device according to claim 1, wherein the coating layer on theplate comprises a molybdenum coating layer.
 3. A driving-wheel bearingdevice according to claim 1, wherein the coating layer on the platecomprises a fluorine-resin coating layer.
 4. A driving-wheel bearingdevice according to claim 1, wherein a film thickness of the coatinglayer on the plate is set within a range from 2 μm to 30 μm.
 5. Adriving-wheel bearing device according to claim 1, wherein a material ofthe plate is stainless steel.
 6. A driving-wheel bearing deviceaccording to claim 1, wherein a yield strength of the plate is set to205 N/mm² or more.
 7. A driving-wheel bearing device according to claim1, wherein the plate is constituted by an annular portion interposedbetween the two opposite surfaces of the shoulder portion of the outerjoint member and the end portion of the inner member and by acylindrical portion formed of a peripheral edge of the annular portion,the peripheral edge being elongated in an axial direction and fitted tothe shoulder portion of the outer joint member.
 8. A driving-wheelbearing device according to claim 1, wherein the plate is constituted byan annular portion interposed between the two opposite surfaces of theshoulder portion of the outer joint member and the end portion of theinner member and by a cylindrical portion formed of a peripheral edge ofthe annular portion, the peripheral edge being elongated in an axialdirection and fitted to the end portion of the inner member.
 9. Adriving-wheel bearing device, comprising: an outer member havingdouble-row outer raceway surfaces formed on an inner periphery thereof;an inner member constituted by a hub wheel and an inner race, the innermember having a wheel attachment flange at one end thereof anddouble-row inner raceway surfaces on an outer periphery thereof; anddouble-row rolling elements interposed between the double-row outerraceway surfaces of the outer member and the double-row inner racewaysurfaces of the inner member, the hub wheel having a shaft hole intowhich a stem section extending from an outer joint member of a constantvelocity universal joint is spline-fitted by being press-fitted,wherein: a plate endowed with predetermined sliding properties bycoating of at least one surface of a substrate is interposed betweenopposite surfaces of a shoulder portion of the outer joint member and anend portion of the inner member; and a surface roughness of thecoating-object substrate is set to be Rz=0.2˜15.0.
 10. A driving-wheelbearing device according to claim 9, wherein a recess groove into whichan inner periphery of the plate is fitted is formed on the shoulderportion of the outer joint member.
 11. A driving-wheel bearing deviceaccording to claim 10, wherein an escape portion is provided at aninnermost part of the recess groove into which the plate is fitted. 12.A driving-wheel bearing device according to claim 9, wherein claw-likeprotrusions are provided on the inner periphery of the plate.
 13. Adriving-wheel bearing device according to claim 9, wherein the plate isendowed with the predetermined sliding properties by being subjected tocoating with a film containing at least one of a fluorine resin andmolybdenum disulfide.
 14. A driving-wheel bearing device according toany one of claim 9, wherein lubricant is interposed in at least one of agap between the plate and the shoulder portion of the outer joint memberand a gap between the plate and the end portion of the inner member. 15.A driving-wheel bearing device according to claim 2, wherein a filmthickness of the coating layer on the plate is set within a range from 2μm to 30 μm.
 16. A driving-wheel bearing device according to claim 3,wherein a film thickness of the coating layer on the plate is set withina range from 2 μm to 30 μm.
 17. A driving-wheel bearing device accordingto claim 2, wherein a material of the plate is stainless steel.
 18. Adriving-wheel bearing device according to claim 3, wherein a material ofthe plate is stainless steel.
 19. A driving-wheel bearing deviceaccording to claim 4, wherein a material of the plate is stainlesssteel.
 20. A driving-wheel bearing device according to claim 15, whereina material of the plate is stainless steel.